Influence of focused fluid flow on the development of submarine lateral spreading. Aguilas high (Gulf of Vera, Western Mediterranean)

The Gulf of Vera (Western Mediterranean) presents a complex geomorphology that is the result of the sedimentary response to the Aguilas tectonic indentation Arc in the framework of the Eurasian–Africa plate collision. This indentation has caused the quasi-continuous oversteepening of the entire margin, which has favored the gravitational instability of the 97% of its seafloor. This margin is one of the most affected by mass movements in the SW Mediterranean Sea. With a characteristic instability of 0.356 km2 and a mean volume of 0.0108 km3, the continental slope shows moderate events comparable to those of other Mediterranean areas. The Aguilas high is one of the structural highs shaping the margin. Its top is characterized by a smooth surface shaped by sedimentary deposits (contourites). Those deposits are affected on the southern edge by a pockform field, erosive features (scars) and deposits with the characteristic ridges of spreading processes. The aim of this work is to define from morphological and geotechnical point of view the instabilities observed on the summit of the high as well as to evaluate the role of fluid flow over those instability processes. Different data set have been merged and combined, including very high-resolution bathymetric data, gravity cores and in-situ geotechnical data (CPTu tests). The results obtained define a geotechnical weak interval at depths between 10 and 15 m below seafloor which is compatible with a detachment surface where lateral spreads developed. The processes would be driven by liquefaction (cyclic softening) triggered by seismic events that affects the clayey sediments present on the stratigraphic record. This process may also favour the vertical fluid flow due to overpressure that may explain the pockform field observed. The spatial association between pockforms and scars observed, evidence a strong link between liquefaction, fluid flow and instability in the study area.   This research was funded by the Spanish MCIN/AEI/10.13039/501100011033. Grant PID2022-138258OB-I00 (inGRAVITAS).